package com.specter.utils;

import java.security.SecureRandom;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;

import lombok.extern.slf4j.Slf4j;

/**
 * Note:AES加密工具类
 * 
 * @author Liang.Wang
 * @version 2010-11-23 下午03:02:36
 */
@Slf4j
public class AESUtils {
	private static final String AES = "AES";

	private static SecretKey KEY = null;

	static {
		try {
			KeyGenerator keygen = KeyGenerator.getInstance(AES);
			SecureRandom sr = SecureRandom.getInstance("SHA1PRNG");
			sr.setSeed(128);
			keygen.init(sr);
			KEY = keygen.generateKey();
		} catch (Exception e) {
			log.error(e.getMessage(), e);
		}
	}

	/**
	 * 加密明文字符串，返回十六进制字符串
	 * 
	 * @param content
	 * @return
	 */
	public static String encrypt(String content) {
		try {
			Cipher cipher = Cipher.getInstance(AES);
			cipher.init(Cipher.ENCRYPT_MODE, KEY);
			byte data[] = content.getBytes();
			// 正式执行加密操作
			byte[] encryptedData = cipher.doFinal(data);
			char[] chars = Hex.encodeHex(encryptedData);
			return new String(chars);
		} catch (Exception e) {
			log.error(e.getMessage(), e);
		}
		return null;
	}

	/**
	 * 把encrypt加密的密文进行解密
	 * 
	 * @param content
	 * @return
	 */
	public static String decrypt(String content) {
		try {
			Cipher cipher = Cipher.getInstance(AES);
			cipher.init(Cipher.DECRYPT_MODE, KEY);
			byte data[] = Hex.decodeHex(content.toCharArray());
			// 正式执行解密操作
			byte[] decryptedData = cipher.doFinal(data);
			return new String(decryptedData);
		} catch (Exception e) {
			log.error(e.getMessage(), e);
		}
		return null;
	}

	public static class Hex {

		/**
		 * Used to build output as Hex
		 */
		private static final char[] DIGITS_LOWER = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c',
				'd', 'e', 'f' };

		/**
		 * Used to build output as Hex
		 */
		private static final char[] DIGITS_UPPER = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C',
				'D', 'E', 'F' };

		/**
		 * Converts an array of characters representing hexadecimal values into an array
		 * of bytes of those same values. The returned array will be half the length of
		 * the passed array, as it takes two characters to represent any given byte. An
		 * exception is thrown if the passed char array has an odd number of elements.
		 * 
		 * @param data An array of characters containing hexadecimal digits
		 * @return A byte array containing binary data decoded from the supplied char
		 *         array.
		 * @throws Exception Thrown if an odd number or illegal of characters is
		 *                          supplied
		 */
		public static byte[] decodeHex(final char[] data) throws Exception {

			final int len = data.length;

			if ((len & 0x01) != 0) {
				throw new Exception("Odd number of characters.");
			}

			final byte[] out = new byte[len >> 1];

			// two characters form the hex value.
			for (int i = 0, j = 0; j < len; i++) {
				int f = toDigit(data[j], j) << 4;
				j++;
				f = f | toDigit(data[j], j);
				j++;
				out[i] = (byte) (f & 0xFF);
			}

			return out;
		}

		/**
		 * Converts an array of bytes into an array of characters representing the
		 * hexadecimal values of each byte in order. The returned array will be double
		 * the length of the passed array, as it takes two characters to represent any
		 * given byte.
		 * 
		 * @param data a byte[] to convert to Hex characters
		 * @return A char[] containing hexadecimal characters
		 */
		public static char[] encodeHex(final byte[] data) {
			return encodeHex(data, true);
		}

		/**
		 * Converts an array of bytes into an array of characters representing the
		 * hexadecimal values of each byte in order. The returned array will be double
		 * the length of the passed array, as it takes two characters to represent any
		 * given byte.
		 * 
		 * @param data        a byte[] to convert to Hex characters
		 * @param toLowerCase <code>true</code> converts to lowercase,
		 *                    <code>false</code> to uppercase
		 * @return A char[] containing hexadecimal characters
		 * @since 1.4
		 */
		public static char[] encodeHex(final byte[] data, final boolean toLowerCase) {
			return encodeHex(data, toLowerCase ? DIGITS_LOWER : DIGITS_UPPER);
		}

		/**
		 * Converts an array of bytes into an array of characters representing the
		 * hexadecimal values of each byte in order. The returned array will be double
		 * the length of the passed array, as it takes two characters to represent any
		 * given byte.
		 * 
		 * @param data     a byte[] to convert to Hex characters
		 * @param toDigits the output alphabet
		 * @return A char[] containing hexadecimal characters
		 * @since 1.4
		 */
		protected static char[] encodeHex(final byte[] data, final char[] toDigits) {
			final int l = data.length;
			final char[] out = new char[l << 1];
			// two characters form the hex value.
			for (int i = 0, j = 0; i < l; i++) {
				out[j++] = toDigits[(0xF0 & data[i]) >>> 4];
				out[j++] = toDigits[0x0F & data[i]];
			}
			return out;
		}

		/**
		 * Converts a hexadecimal character to an integer.
		 * 
		 * @param ch    A character to convert to an integer digit
		 * @param index The index of the character in the source
		 * @return An integer
		 * @throws Exception Thrown if ch is an illegal hex character
		 */
		protected static int toDigit(final char ch, final int index) throws Exception {
			final int digit = Character.digit(ch, 16);
			if (digit == -1) {
				throw new Exception("Illegal hexadecimal character " + ch + " at index " + index);
			}
			return digit;
		}
	}

}
